1. Field of the Invention
The present invention relates to a semiconductor light-emitting device made of a group III-nitride compound semiconductor.
2. Description of the Related Art
A conventional semiconductor light-emitting device made of a group III-nitride compound semiconductor includes, in order of mention, a buffer layer and a semiconductor layer having a light-emitting region on a substrate made of a material such as SiC. The semiconductor light-emitting device further includes a multi-layered reflective layer between the substrate and the semiconductor layer in order to improve the emission efficiency of light produced in the light-emitting region. Of the light produced in the light-emitting region, light directed toward the substrate is reflected from the multi-layered reflective layer, whereby the emission efficiency is improved.
However, the multi-layered reflective layer cannot reflect 100% of the light produced in the light-emitting region, and allows several % of the light to leak through the lower boundary surface of the multi-layered reflective layer. In the case where a substrate made of SiC is used as the substrate, the light leaked from the lower boundary surface of the multi-layered reflective layer propagates in the substrate to be reflected from the lower boundary surface of the substrate. Further, the light reflected from the lower boundary surface of the substrate interferes, at the upper boundary surface of the substrate, with the light leaked from the lower boundary surface of the multi-layered reflective layer.
Accordingly, depending on the thickness of the substrate, the light reflected from the lower boundary surface of the substrate and the light leaked from the lower boundary surface of the multi-layered reflective layer interfere with each other at the upper boundary surface of the substrate, and this causes a decrease in the light emission efficiency. In the conventional semiconductor light-emitting devices made of group III-nitride compound semiconductors, there may be cases where light emission efficiency significantly decreases because of lack of knowledge about substrate thickness.